The invention pertains to a device and a method for accurately measuring the geometric characteristics of terrain by tracing the profile of the land surface with a wheeled instrument.
The manually operated engineer""s wheel is a classic tool of the surveyor""s art. Typically, this instrument is a pole with an affixed handle at one end and a wheel with an odometer at the other end, with either a mechanical (U.S. Pat. No. 275,734) or electronic (U.S. Pat. No. 4,409,663) odometer.
The engineer""s wheel is often used in the conjunction with other measuring instruments to produce a geometric representation of the terrain. Manual surveying is a time consuming and expensive process requiring a highly trained person.
Methods have been developed for automatic surveying of very large plots of land using motorized land vehicles, such as disclosed in U.S. Pat. No. 5,174,038, or aircraft, such as disclosed in U.S. Pat. No. 5,557,397, which naturally require very expensive equipment and highly skilled operators. Such large scale systems may depend on satellites, say via GPS or DGPS or photogrammetry (U.S. Pat. No. 5,517,419).
Small scale automated surveying systems, such as disclosed in U.S. Pat. No. 5,956,660 or German patent DE 19729355, based on inertial dead reckoning are subject to error accumulation, and so have limited practical value.
A useful addition to the engineer""s wheel would be the ability to keep a precise record of its direction in a two-dimensional plane along with the distance traveled. Then areas and non-linear contours could be measured when a computer processed the data collected. Also, obstacles such as ponds, fences, trees and brush could be avoided when measuring a straight-line distance between two points. Several attempts have been made in this direction:
German patent DE4036424 discloses a three-wheeled device designed for flat terrain. The device contains two coaxial measuring wheels, which is sufficient to determine the contour of travel in the plane of motion of the device, subject to the usual error accumulation problem. An addendum to this patent, DE4115809, claims that, with the addition of an inclinometer along its forward axis, that device would have the capability to measure changes in elevation as well, but this will only be the case if the device moves directly up or down hill without moving across the grade in the slightest, which is a severe limitation.
Another attempt to measure contours is disclosed in German patent DE3925133, which, instead of a wheel, uses a ball that is able to roll in any direction on the surface to be surveyed. During its motion, this ball must maintain physical contact with the balls of two fixed computer mice. This device, besides being difficult and expensive to produce and maintain, is impractical and unsuitable for work outdoors since the dirt and moisture which comes in contact with the rolling ball is transferred to the bearings and the mice. Even in a clean environment, the device will suffer from the usual error of accumulation.
World patent WO9627779 discloses a method of profiling terrain with a device supported by at least one wheel equipped with an odometer, together with a single direction sensor to determine the direction of the wheel. To be practical, the guide-pole must be able to tip from side to side as well as rotate freely about the axle of the measuring wheel. A device with two degrees of freedom like a traditional measuring wheel needs two attitude sensors to properly report its orientation with respect to the world. A single direction sensor is not enough unless some assumptions are made about the pitch, roll or yaw of the device. The device of WO9627779 assumes that there is limited freedom of movement as there is only one incline angle detected for correcting the compass. There is also no method given for dealing with the effects of inertia, which will significantly corrupt the azimuth when the device is accelerated and decelerated.
The invention pertains to a device and method for making useful measurements of terrain features using a measuring wheel, two attitude sensors and a computing device.